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In Vivo Cotton Stem and Petiole Nitrate Reductase Activity

USDA-ARS Irrigated Desert Res. Stn., 4151 HWY 86, Brawley, CA 92227
USDA-ARS Western Cotton Res. Lab., 4135 E. Broadway, Phoenix, AZ 85040

^* Corresponding author.

Cotton (Gossypium hirsutum L.) plant stems and petioles are not generally considered to be major sites of nitrate reductase activity (NRA). Field studies were conducted to determine the significance of stem NRA and the potential of petiole NRA as an indicator of the N status of cotton. The contribution of various cotton plant parts to the in vivo plant shoot NRA (with endogenous nitrate only) was evaluated at five stages of plant development from the seedling stage to the flower bud stage (reproductive stages). In 1987 and 1988, samples were taken between 1000 and 1200 h under a clear sky from various plant parts of cotton (cultivar Deltapine 61) grown in a calcareous Holtville silty clay in the Imperial Valley, CA. Results showed that the plant stem (or hypocotyl) plus petiole contribution to the total plant shoot NRA increased from 14 to 72% as the plant progressed from vegetative growth to reproductive growth. Results indicated that cotton plants stems were high in NRA relative to leaf blades, except at the seedling stage. Samples taken from 35 cultivars and breeding lines in the same year under the same environmental conditions showed that the petiole NRA was high at the early flower bud stage. The petiole's average contribution of 52% of the total NRA of the top mature leaf indicates that petiole NRA may be useful as an indicator of N metabolism at the early flower bud stage of development.

Received for publication March 8, 1989.